An eccentric screw pump is a displacement pump in which a rotating part, the rotor, moves inside a fixed part, the stator or stator housing. The rotor performs a rotational movement as well as an overlapping radial movement, and thus moves along a circular path while additionally turning about its own axis. The rotor comprises around the outer circumference a type of knuckle thread bolt with a steep pitch which moves inside a cavity in the stator, which is designed such that the movement of the rotor in the stator causes conveyor spaces to move from the inlet side to the outlet side. Typically, the inlet side of the stator/rotor assembly of an eccentric screw pump comprises a feeding chamber for the fluid to be pumped, which is fluidly connected to the stator inlet opening. A drive shaft which, due to the rotor movement, has to perform a wobbling movement, is turning inside this feeding chamber. This drive shaft is typically formed by two cardan joints connected via a wobble shaft and is directly or indirectly coupled with the drive motor on the side opposite from the rotor.
On the inlet side, eccentric screw pumps are typically connected with a feeding pipe via which the fluid to be pumped is fed to the stator housing inlet opening. On the outlet side, eccentric screw pumps are connected with an outlet pipe via which the pumped fluid is conducted away. Generally, eccentric screw pumps are suitable for pumping media in both directions. Accordingly, for the purpose of this disclosure, it is also possible for the conveying direction to be reversed with a corresponding functional switching of the stator inlet opening and the stator outlet opening.
Eccentric screw pumps are suitable for pumping a great variety of very different fluids. This includes, in particular, thick and viscous media which may also contain solids having an abrasive effect.
Generally, but in particular when using an eccentric screw pump to pump fluids in the form of solids-containing media, wear of the stator and possibly also wear of the rotor means that the stator, and possibly also the rotor, will need to be replaced in regular maintenance intervals. For this purpose, the rotor must be disconnected on the drive side and the flange connections of the stator housing must be separated in order to create space to remove the rotor from the stator or to remove the entire rotor-stator unit. This process is regularly time-consuming and costly; due to the considerable weight of the stator and, in particular, the stator-rotor unit, it is also difficult and can be accomplished only with specific tools and a lifting device. The downtime of an eccentric screw pump caused by such necessary maintenance can easily run between several hours to one day. From DE 10 2008 021 919 we already know an eccentric screw pump in which a spacer ring is arranged between the stator and a connection piece for an outlet pipe. By removing this spacer ring, disassembling the stator becomes easier, because once the rotor has been disconnected from the cardan joint, it allows for the rotor to be swung out along with the stator. A disadvantage of this design is the required disconnection of the rotor from the cardan joint for this swiveling movement, which requires a difficult maintenance operation. Another disadvantage of this design is that it creates additional sealing surfaces in the area of the stator outlet opening, i.e. on the pressure side of the eccentric screw pump, which causes a risk of leakage. Moreover, it is disadvantageous that in case of blockage by foreign objects in the area of the outlet opening the removal of the spacer ring may also be blocked by such foreign objects. This could hinder or make impossible the removal of the spacer ring so that, as a result, the maintenance work can no longer be performed in this form.